1. Field of the Invention
The present invention relates to clocks and clock radios, and more specifically to a transformerless LED digital alarm clock and LED clock radios using AC line voltage as a primary source of power which is converted to low voltage DC power useful for both running the clock and charging a backup battery. The digital clock uses a programmable microprocessor to provide the display control signals for four individual digit displays such that the "ON" time or duty cycle for each digit begin displayed is at a minimum.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Over the years the modern world has required higher and higher levels of interaction and interdependence of mankind. In addition, people seem to be performing many more of their activities or tasks during both the day and night. To be able to get all of these tasks and activities accomplished, a greater and greater premium has been placed on punctuality. For example, most activities start at a preset time and tardiness with respect to the activity may have little effect or sometimes disastrous effects. In addition, because of the international element of business, some business meetings such as teleconferencing may take place at any time during the 24 hour day, and travel or transportation for meetings, vacations, etc., may also start and/or terminate at almost any hour.
In any event, time awareness cannot be avoided and the problem of being awakened from a sound sleep has become more and more critical. At the same time, since being awakened artificially almost every morning has become commonplace, clocks used for awakening someone have evolved from the strident sound of the "alarm clock" to the more acceptable and less traumatic wakening to music, news or other pleasant sounds. Modern digital alarm clocks or clock radios also provide LED's (light emitting diodes) for a visual indication of the time even at night. Also, of course, energy conservation in every field is encouraged and some types of clocks such as analog quartz clocks or electronic digital clocks are specifically desirable as they typically have long life and require very little energy to function. Unfortunately, even though the total amount of energy used is small, they do require a constant supply of electrical power to run, and an uninterrupted source of power if they are to remain accurate. Such power sources simply do not exist. Batteries in battery powered devices or clocks run out or "die" and commercially available line AC power supplied to the home and business are occasionally interrupted by a myriad of causes. In addition, techniques for improving the efficiency and dependability of time keeping systems such as alarm clocks, clock radios, etc., are always being sought.
For example, U.S. Pat. No. 4,697,930 to Roberts et al. and entitled "Transformerless Clock Circuit With Duplex Optoelectronic Display" discloses a transformerless power supply and display energizing circuit for a clock circuit with a duplex optoelectronic display driven by low voltage integrated clock circuit. The clock circuit has positive and negative voltage input terminals and the duplex display has a first terminal connected to a first common cathode and a second terminal connected to a second common cathode of the display. The transformerless circuit is powered from an AC source. An impedance, which may be either resistive or reactive, reduces the AC voltage to a level suitable for the integrated clock circuit. The transformerless circuit also generates synchronous DC level-shifted pulse trains for driving the positive input terminal of the integrated clock circuit alternately between a first voltage and a reference voltage while synchronously driving the display first terminal between the first voltage and a voltage of equal amplitude and opposite polarity.
U.S. Pat. No. 4,595,861, issued to Simopoulos et al. and entitled "Power Supplies for Electroluminescent Panels" discloses circuitry for converting a DC power supply to an AC power supply for electroluminescent lamps which are selfinhibited from further oscillations and are current limited in the event that a failure occurs in an EL (electroluminescent) lamp which results in the EL lamp being shorted. According to one embodiment of this patent, a single ended and push/pull transformer power supply is disclosed and according to a second embodiment, a transformerless solid state power supply is disclosed. The solid state power supply uses a voltage multiplier to increase the AC or square wave voltage to a level of almost 140 volts for powering the EL lamp. Thus, it is seen that the circuitry in this patent discloses techniques for converting from DC power to AC power, not AC power to DC power and further provides circuitry to inhibit oscillations and operations of the circuitry in the event of a shorting of the EL lamp or a substantial voltage drop.
U.S. Pat. No. 4,201,039, to Roland M. Marion and entitled "Numerical Display Using Plural Light Sources and Having a Reduced and Substantially Constant Current Requirement" discloses a numerical digital display having a reduced DC current requirement per character display site. The circuitry is useful for powering a digital display in an AC powered clock or clock radio in which it is desirable to keep the DC current requirement of the display to a substantially constant minimum suitable for use with a low cost transformerless power supply conventional with radio receivers. The current requirements of the digital character display site is reduced over that of full parallel operation by selectively serializing certain light sources in a manner leaving the display control circuitry uncomplicated by permitting each light source state to be controlled by a shunt control switch sharing a common bus. The shunt control, which diverts rather than prevents current flow in the display, allows the display current to remain substantially constant irrespective of the digital numbers displayed.
U.S. Pat. No. 4,109,180 to Ogle et al., and entitled "AC-Powered Display System With Voltage Limitation" discloses an AC-powered display system which includes a gas discharge display panel, an integrated circuit, and a limiting network. The integrated circuit is provided as a display pattern controller and may also comprise a digital alarm clock circuitry which provides outputs for controlling the gas discharge display panel. The circuitry also includes a limiting network which reduces the current through the system in response to an excessive voltage across the controller. U.S. Pat. No. 4,063,234 to Arn et al. and entitled "Incandescent, Flat Screen, Video Display" discloses a flat screen video display comprising a plurality of incandescent lamps arranged in an addressable X-Y matrix. The circuitry also provides a memory and driver circuit for each individual incandescent lamp for use in a flat screen video display apparatus.
U.S. Pat. No. 3,602,795 to John B. Gunn and entitled "Transformerless Power Supply" discloses circuits for converting an input voltage from a high amplitude to a lower amplitude DC voltage.